This invention relates to silicone rubber compositions of a non-fluidity type, which have superior workability and formability and further are capable of producing silicone rubber cured products which form elastomers with an extremely low hardness.
Silicone rubber compositions are usually prepared by the addition of fillers, process assisting agents and vulcanization agents into silicone polymers (a raw rubber). The cured products of such silicone rubber compositions (silicone rubbers) are superior in heat resistance, weather resistance, durability, mold releasing characteristics, and electrical properties. Therefore, they are processed and finished into many shapes and are utilized in various fields as construction materials, electric and electronic parts, automotive parts, OA instrument parts, and domestic wares including food containers, rice cookers and insulated containers.
Application of silica as a filler, in this case, provides a reinforcing effect, resulting in silicone rubbers with superior physical properties. An increased ratio of the silica fillers improves the physical properties; however, it also increases the hardness of the silicone rubber products. Recently, lower hardness (JIS-A hardness of at most 40) silicone rubbers, which are obtained by the curing of silicone rubber compositions with a very small amount of reinforcing silica fillers, were found to possess superior flexibility and rubber elasticity. These characteristics are difficult to achieve with the conventional high hardness silicone rubbers; therefore, these lower hardness silicone rubbers have begun to be utilized as a raw material for rolls, vibration controllers, and vibration preventers.
However, the reduced amount of reinforcing silica fillers not only makes the silicone rubber compositions more sticky and lowers their roll workability, but also causes fluidity in the compositions and lowers the formability, for example, by making uniform extrusion molding more difficult.